Japanese knotweed Fallopia japonica (Houtt.) R. Decr. or Polygonum cuspidatum Sieb. & Zucc. Giant knotweed Fallopia sachalinensis (F. Schmidt ex Maxim.) R. Decr. or Polygonum sachalinense F. Schmidt ex Maxim. Bohemian knotweed Fallopia × bohemica (Chrtek & Chrtková) J. P. Bailey or Polygonum ×bohemicum (J. Chrtek & Chrtkovß) Zika & Jacobson [cuspidatum ×sachalinense] Family: Polygonaceae Synonyms for Fallopia japonica: Pleuropterus cuspidatus (Sieb. & Zucc.) Moldenke, P. zuccarinii (Small) Small, Polygonum cuspidatum Sieb. & Zucc. var. compactum (Hook. f.) Bailey, P. zuccarinii Small, Reynoutria japonica Houtt. Other common names: Japanese bamboo, fleeceflower, Mexican bamboo Synonyms for Fallopia sachalinensis: Reynoutria sachalinensis (F. Schmidt ex Maxim.) Nakai, Tiniaria sachalinensis (F. Schmidt) Janchen Other common names: none Synonyms for Fallopia x bohemica: none Other common names: none Invasiveness Rank: 87 The invasiveness rank is calculated based on a species’ ecological impacts, biological attributes, distribution, and response to control measures. The ranks are scaled from 0 to 100, with 0 representing a plant that poses no threat to native ecosystems and 100 representing a plant that poses a major threat to native ecosystems. Description Japanese knotweed is a perennial plant that grows from long, creeping rhizomes. Rhizomes are thick, extensive, and 5 to 6 meters long. They store large quantities of carbohydrates. Stems are stout, hollow reddish-brown, swollen at the nodes, and 1 ¼ to 2 ¾ meters tall. Twigs often zigzag slightly from node to node. Leaves are alternate, 5 to 15 cm long, and broadly ovate with more or less truncate bases and acuminate tips. They have short petioles. Plants are dioecious, with male and female flowers on separate plants. Inflorescences are many-flowered, branched, open, and lax. Flowers are approximately 2 mm long. Japanese knotweed is pollinated by insects (Whitson et al. 2000). Similar species: All native species of Polygonum in Alaska are considerably smaller and lack broad leaves. Giant knotweed has more heart-shaped leaf bases and less tapered leaf tips than Japanese knotweed (Zika and Jacobson 2003). Bohemian knotweed may also occur in Alaska. It is a hybrid between Japanese knotweed and giant knotweed. Inflorescences and foliage of Fallopia japonica (Houtt.) R. Decr. Last Updated: 2011-02-07 by Helen Klein http://aknhp.uaa.alaska.edu Role of disturbance in establishment: Japanese knotweed can establish in natural habitats with little or no observable disturbance. Potential for long-distance dispersal: Plant fragments can be washed downstream where they are capable of producing new colonies. Dispersal across marine waters has also been reported (Beerling et al. 1994). Fruits can be dispersed by wind. Potential to be spread by human activity: Japanese knotweed has been cultivated as an ornamental plant in southeast Alaska and the Anchorage area. It commonly escapes from gardens. Rhizome fragments can be transported on construction and maintenance equipment. Germination requirements: Germination rates are high after either 5 months of storage at room temperature or 3 months of storage at 2°C to 4.5°C. Growth requirements: Japanese knotweed has been observed growing in a variety of soil types, including silt, loam, and sand, with pH between 4.5 and 7.4. It can tolerate high temperatures, salinity, and drought, but it is shade intolerant (Saiger 1991). Congeneric weeds: Prostrate knotweed (Polygonum aviculare), Asiatic tearthumb (P. perfoliatum), Himalayan knotweed (P. polystachyum), black bindweed (Fallopia convolvulus / Polygonum Infestation of Fallopia japonica (Houtt.) R. Decr. convolvulus), spotted ladysthumb (Persicaria maculosa / Polygonum persicaria), and curlytop knotweed Ecological Impact (Persicaria lapathifolia / Polygonum lapathifolium) are Impact on community composition, structure, and considered noxious weeds in one or more states of the interactions: Japanese knotweed forms monocultures U.S. or provinces of Canada (USDA, NRSC 2006, that reduce plant species diversity by shading native Invaders 2010). A number of Polygonum species that vegetation. It clogs waterways and lowers the quality of are native to North America have weedy habits and are habitat for wildlife and fish. It reduces the food supply listed as noxious weeds in some American states. The for juvenile salmon in the spring. Japanese knotweed species listed above are closely related taxa and can be hybridizes with giant knotweed (Saiger 1991). considered congeneric weeds, although the latest Impact on ecosystem processes: Japanese knotweed taxonomy considers them to be members of three increases the risk of soil erosion. Dead stems and leaf different genera: Polygonum, Fallopia, and Persicaria litter decompose very slowly and form deep organic (FNA 1993+). layers. These thick layers prevent native seeds from germinating and thus alter the natural successional Legal Listings for Japanese knotweed processes of native plant species. During dormant Has not been declared noxious periods, dried stems and leaves and can increase the risk Listed noxious in Alaska of fires. Listed noxious by other states (AL, CA, OR, VT, WA) Federal noxious weed Biology and Invasive Potential Listed noxious in Canada or other countries Reproductive potential: Japanese knotweed reproduces sexually by seeds and vegetatively from rhizomes. Very Legal Listings for giant knotweed small fragments of rhizomes (consisting of as little mass Has not been declared noxious as 700 mg) can produce new plants. Seed production in Britain varies from none, when fertile male plants are Listed noxious in Alaska rare, to several hundred per plant, when plants grow in Listed noxious by other states (CA, OR, WA) close proximity to Bukhara fleeceflower (F. Federal noxious weed baldschuanica) or giant knotweed (Beerling et al. 1994). Listed noxious in Canada or other countries No systematic study of seed longevity has been undertaken, but seeds stored at room temperature Legal Listings for Bohemian knotweed remained viable for four years. Has not been declared noxious Last Updated: 2011-02-07 by Helen Klein http://aknhp.uaa.alaska.edu Listed noxious in Alaska Listed noxious by other states (WA) Pacific Maritime Federal noxious weed Interior-Boreal Listed noxious in Canada or other countries Arctic-Alpine Collection Site Distribution and Abundance Japanese knotweed grows in damp areas, riverbanks, waste places, roadsides, neglected gardens, and old home sites (Beerling et al. 1994). Native and current distribution: Japanese knotweed is native to Japan, northern China, Taiwan, and Korea. It Distribution of giant knotweed in Alaska. was introduced to North America in the late 19th century. Japanese knotweed grows in much of Canada Management and 41 states of the U.S. (USDA, NRCS 2006). It is also Control methods are expensive and extremely labor a serious invasive plant in Europe, the United Kingdom, intensive. Grubbing and hand pulling can effectively and New Zealand. In Europe, the northern limit of control small populations. Mechanical methods distribution for Japanese knotweed corresponds with the followed by herbicide treatments have proven somewhat boundary of no fewer than 120 frost-free days (Beerling successful in heavily infested areas. Herbicide et al. 1994). Japanese knotweed has been documented treatments must be repeated four or more times per from the Pacific Maritime and Interior-Boreal season for several years to eradicate infestations. ecogeographic regions of Alaska (AKEPIC 2010, UAM Controlled areas should be monitored for at least one 2010). Giant knotweed has been documented from the growing season after the completion of treatment Pacific Maritime ecogeographic region (AKEPIC 2010, efforts. No biological control agents are currently UAM 2010). available. Pacific Maritime Interior- Boreal Arctic-Alpine Collection Site Distribution of Japanese knotweed in Alaska. References: AKEPIC database. Alaska Exotic Plant Information Invaders Database System. 2010. University of Clearinghouse Database. 2010. Available: Montana. Missoula, MT. http://akweeds.uaa.alaska.edu/ http://invader.dbs.umt.edu/ Beerling, D.J., J.P. Bailey, A.P. Conolly. 1994. Fallopia Seiger, L. 1991. Element Stewardship Abstract for japonica (Houtt.) Ronse Decraene. Journal of Polygonum cuspidatum. The Nature Ecology. 82 (4): 959-979. Conservancy in collaboration with the eFloras. 2008. Published on the Internet International Network of Natural Heritage http://www.efloras.org [accessed 22 September Programs and Conservation Data Centers. 2010]. Missouri Botanical Garden, St. Louis, Natural Heritage Databases. Arlington, VA. MO & Harvard University Herbaria, UAM. 2010. University of Alaska Museum, University Cambridge, MA. of Alaska Fairbanks. Available: Flora of North America Editorial Committee, eds. http://arctos.database.museum/home.cfm 1993+. Flora of North America North of USDA, NRCS. 2006. The PLANTS Database, Version Mexico. 7+ vols. New York and Oxford. 3.5 (http://plants.usda.gov). Data compiled from various sources by Mark W. Skinner. Last Updated: 2011-02-07 by Helen Klein http://aknhp.uaa.alaska.edu National Plant Data Center, Baton Rouge, LA Extension Services. University of Wyoming. 70874-4490 USA. Laramie, Wyoming. 630 pp. Whitson, T.D., L.C. Burrill, S.A. Dewey, D.W. Cudney, Zika, P.F. and A.L. Jacobson. 2003. An overlooked B.E. Nelson, R.D. Lee, R. Parker. 2000. Weeds hybrid Japanese knotweed (Polygonum of the West. The Western Society of Weed cuspidatum x sachalinense); Polygonaceae) in Science in cooperation with the Western United North America. Rhodora 105: 143-152. States Land Grant Universities, Cooperative Last Updated: 2011-02-07 by Helen Klein http://aknhp.uaa.alaska.edu .